Super high frequency filter



Aug- 23, 1949. E. G. UNDER A 2,479,687

SUPER HIGH FREQUENCY FILTER Filed May 17, 1943 Effnz al;

(Ittorneg Patented Aug. 23, 1949 SUPER HIGH FREQUENCY FILTER Ernest G. Linder, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 17, 1943, Serial No. 487,250 4 Claims. (Cl. 178-44) This invention relates generally to super-high frequency apparatus, and more particularly to filters for attenuating super-high frequency energy on electrical power conductors or movable or rotating shafts.

Briefly, the invention contemplates the use of quarter-wave filter sections for attenuating super-high frequency energy on power conductors or rotating shafts which extend through super high frequency shielding enclosures. The invention comprises a unique super-high frequency bypass device which offers extremely low shunt impedance to super-high frequency currents impressed thereon. The purpose of the filters is effectively to ground the super-high frequency energy at one or more points along a conductor at which super-high frequency voltage loops occur. The conductor is effectively grounded through a length equal to at least a quarter wavelength at the superhigh operating frequency, whereby some point or points along the conductor will necessarily correspond to the occurrence of a voltage loop. This arrangement may be advantageously adapted to devices operating over a relatively wide range of frequencies, since the bypassing will be uniform and equally effective notwithstanding changes in, the standing wave distribution along the line.

One of the several modifications of the invention. to be described in detail hereinafter, includes a quarter-wave bypass capacitor for filtering power leads extending through a shielding super-high frequency enclosure.

A second modification includes a more complex quarter-wave filter which comprises a central conductor coaxially disposed with respect to an outer cylindrical conductor, which is spaced therefrom a distance of the order of a quarter wavelength at the operating frecuency. Insulation for direct current is'provided between the conductors. and the outer cylindrical conductor is effectively grounded to the shielding enclosure and the shielding braid on the conventional power conductors. A plurality of annular conductive elements are interposed between the central conductor and the outer coaxial conductor at intervals of the order of a quarter wavelength wthin the operating super-high frequency range. The peripheries of the annular conduc- 'tive members are in close capacitive relationwith the inside surface of the outer concentric conductor, thereby providing extremely low impedance shunt circuits for the super-high frequency energy at intervals of the order of a quarter Wavelength along the central conductor.

A third embodiment of the invention comprises means for effectively grounding a movable or rotating shaft which extends through an aperture in a super-high frequency shielding enclosure. A cylindrical outer conductor, securely fastened to the shielding enclosure, includes at each end thereof bearing members for the shaft. Interposed between the bearing members, at intervals of the order of a quarter wavelength at the operating frequency, are a plurality of annular substantially quarter wave conductive elements securely fastened to the movable or rotating shaft. The peripheries of these annular conductive elements are in close capacitive relation with the outer cylindrical conductor, which is effectively grounded to the shielding enclosure. If preferred. the complete lter may be constructed as a unit, and may include means for coupling the rotating or movable shaft to the inner and outer extremities of the central movn able conductor of the filter.

Among the objects of the invention is to pro`1 vide improved means for filtering super-high frequency energy. Another object is to provide an improved quarter wavelength filter for power rleads extending into a super-high frequency Shielding enclosure. A further object is to provide an improved quarter wavelength super-high frequency filter which includes a plurality of capacitive bypass elements at intervals of the order of a quarter wavelength at the operating frequency. A still further object of the invention is to provide an improved lter for super-high frequency shielding enclosure. An additional object is to provide an improved super-high frequency filter for conductive elements extending into a shielding super-high frequency enclosure, which includes a plurality of capacitive elements separated a distance of the order of a quarter wavelengths at operating frequencies extending over a predetermined frequency band,

The invention will be described in further detail by reference to the accompanying drawing, of which Figure l is a cross-sectional view of one embodiment of the invention, Figure 2 is a crosssection-al View of a second embodiment thereof, and Figure 3 is a crosssectional View of a third embodiment thereof. Similar reference numerals are applied to similar elements throughout the drawing.

Figure 1 comprises a unique bypass capacitor I, which may be employed to remove substantially all traces of super-high frequency energy from D.C. or low frequency power leads 2, 3 which extend into a shielding enclosure including an enclosure wall 4. The capacitor VI comprises a block of brass, aluminum or similar material 5, having two holes drilled therethrough. The dimension of the block 5 and the thickness of the enclosure wall 4 along the axis of the holes is approximately a quarter wavelength at the average operating frequency. As a matter of convenience, its width may be of the same order, while its length is of any convenient dimension, which will depend upon the number of conductors to be filtered. It will be understood that any number of iilter sections may be provided, although only two have been illustrated.

The metal block 5 maybe securely mounted on the wall 4 of the shielding enclosure in any manner which provides good electrical contact therewith. Each conductor passes through one of the holes provided in the brass block. To increase the capacity between the conductors and the grounded block, capacitive discs 5 may be soldered to the leads adjacent each surface of the block` and insulated therefrom by suitable insulators I of mica, or the like.

The purpose of this arrangement is to make certain ,that theY leads are grounded at a point which is not ,a Voltageinode. Since the leads are effectively grounded through a` length equal to a Vquarter wavelength at the average operating frequency, some point within the block will necessarily be that corresponding to a voltage loop, and ,hencethe grounding will be effective. This arrangementis particularly advantageous where thedevice is operated over a wide range of frequencies, since Ythe bypassing will be uniform and equally effective V,notwithstanding variations in the. standing` wave distribution along the lines.

Figure 2 comprises `a quarter-wave lter for a powergconductor extending into a shielding super-highfrequency enclosure, wherein a plurality of quarterwave capacitive elements are provided effectively to bypass any super-high frequency energy which would normally follow the power conductor. A shielded power conductor includes a central conductor II, an insulating layer I2, and an external shield I3 which may be in the form of a layer of lead or a layer of woven Ametallic braid. The iilter includes `a central conductor I4, to the extremities Vof which the power conductors II, II are soldered or attached in any other convenient manner. The central filter conductor I4 is surrounded by a concentric cylindrical conductor I5, which is se'- vcurely supported andgrounded vby the apertured enclosure wall 4.

The central conductor I4 and the outer cylindrical conductor VI5 are supported in concentric Similarly, a conductive Asleeve 24 extends, from the metallic member I'I, a short distance along the shielding sleeve 'I3' of the internal power conductor.

A plurality of metallic discs 22, 23, 24 are dis- Aposed longitudinally along the central conductor I4, intermediate the annular supporting members I6, I'I. The 'metallic discs 22, 23, Z4 are spaced from the annular supportingmembers I6, I1, and from each other distances of the order of a quarter wavelength within Vthe band of supere'high Voperating frequencies. If' filtering is desired over a, relatively wide frequency band, the relative spacing of the metal discs 22, 23, 24 may be varied x0 7o x2 E 4 to extend the filter attenuation characteristics. The peripheries of the metal discs 22, 23, 24 are in-close capacitive relation with the internal surface of the outer cylindrical conductor I5. It will be seen that the several shunt capacitances provided thereby will be disposed at intervals of the order of a quarter wavelength along the lter section; whereby standing waves of the order of the operating frequencies will be attenuated effectively.

Figure v3 is similar to Figure 2, in that a plurality o`f capacitive elements are arranged at intervals of the order of a quarter wavelength between a central conductor and an outer cylindrcal conductor substantially concentric therewith and electrically grounded thereto. This modicationprvides a convenient and effective means for filtering and bypassing Asuper-high frequency energy on a rotating or otherwise movable shaft extending into` a shielding super-high frequency enclosure, Theouter cylindrical conductor I5 is securely supported by and electrically connected to thev wall 4 of the shielding enclosure. The annular conductive elements I6, I'I provide bearings for supporting a central cylindrical conductor 2lil substantially coaxially with the outer cylindrical conductor I5. The central cylindrical Aconductor 26 may include threaded holes 2'I at eachend thereof to receive complementarily `threaded portions of the rotating shafts 28, 28'.y

Effective filtering of Vsuperi-high frequency energy which penetrates.the bearingsV I6, I'I is providedk by a pluralityof substantially quarter wave metallic discs 222, 23, *24 attached Yto the central cylindrical conductor Zgel-Svillltelvals of the order of a quarter lwavelengtlfi f a it avgz'- at the operating super-high frequency. The peripheries of the "metallicdiscs 22,v 23, 24 are in close capacitive relation 'with the Vinside surface vof the outer cylindrical conductor I5 and operate in a manner similarto that described for the device of Fig. 2. u A l Thus the invention described comprisesthree embodiments of quarter wave .super-high frequency filters for eiectively bypassing superhigh frequency energy -on power conductors yor Arotating elements extendingyintoshielding superhigh frequencyenclosures.

What I claim is:

1. A filter'for-superfhigh*frequency energy incl-uding -a central conductor, fa cylindrical conductor concentric with Asaid Ycentral r'sonductor iand spacedftherefroin ia`- distance Aof the order of one quarter wavelength at the operating frequency, annular conductive V'members adjacent each end of said cylindrical 'conductor supporting Vsaid conductors infsaid relatively `concentric relation,'-a;nd fat` least one annular conductive element Aconnected to and supported by said central conductor intermediate said 'annular members and capacitivelycoupled-'to'said cylindrical conductor.

42. Apparatus :'-according f'to claim 1 yincluding means for'movingfsaidV inner conductor with respect to said outerccaxiallyfdisposedconductor.

3. A lter for super-high frequency energy including a movable central conductor, a cylindrical conductor concentric with said central conductor and spaced therefrom a distance of the order of one quarter wavelength at the operating frequency, annular conductive bearing members adjacent each end of said cylindrical conductor supporting said conductors in said relatively concentric relation, and at least one annular conductive element connected to and supported by said central conductor intermediate said annular members and capacitively coupled to said cylindrical conductor.

4. Apparatus according to claim 1 including a. plurality of said capacitive annular elements spaced the order of one-quarter wavelength at `a plurality of attenuated operating frequencies of said energy.

ERNEST G. LINDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

